Peterson initially joined Glasgow on a two year deal in 2015. He extended that by another two years keeping him at Scotstoun until May 2019 when he moved to Bayonne and then Newcastle where he spent four seasons.
Greg has been capped by the USA and joined Leicester Tigers in December from Super Rugby side, NSW Waratahs. He has played three times for the Aviva Premiership side.
The Australian-born lock, who was with the Waratahs for five years after joining their Academy in 2009, has made one Super Rugby appearance.
In 2010, he made his Shute Shield debut for Manly, making his mark by winning the 2010 Shute Shield Rookie of the Year award in his first year out of school.
The towering forward, who stands at 6 foot 8 and weighs more than 19 stone, represented Australia U20s on eight occasions.
Peterson comes from a rich athletic background with his father having played American Football for Northwestern University in Chicago and his grandfather having played in one of the first ever rugby union games in the United States.